1. Field of the Invention
The present invention generally relates to an image forming apparatus, and more particularly is directed to an image forming apparatus which automatically determines the state and condition of image forming elements within the apparatus. When necessary, the image forming elements are initialized to a desired state.
2. Description of the Related Art
An image forming apparatus, such as a copier or laser printer, employs electrophotographic image forming techniques. Using these techniques, a latent image is formed on a photosensitive drum. A developing device develops the latent image using a toner which makes the latent image visible. A problem arises, however, in that it is difficult to convey only the toner to the photosensitive drum during the developing process.
Thus, a toner carrier, such as a magnetic powder, is used which allows only the toner to be easily conveyed in order to form a high quality image. However, it is necessary to mix the toner and toner carriers together before forming the image.
The toner is consumed during every image formation so that it is necessary to re-supply the toner after a plurality of images are formed. As is well known, a toner sensor automatically detects the quantity of residual toner, i.e., the density of the toner, in the developing device. The toner sensor generates a signal indicating that toner density is equal to or less than a predetermined value. Thus, the image forming apparatus supplies toner to the developer in response to the density signal. It is important to determine the predetermined density value in order to adequately supply the toner. Usually, the predetermined value is determined on the basis of an initial value of toner density.
It is necessary to mix the toner and the toner carriers together in order to correctly measure the initial value. This is because the toner sensor measures toner density on the basis of the magnetic characteristic of the mixture of the toner and the toner carriers.
A conventional image forming apparatus performs an initial operation to mix together the toner and the toner carriers and to determine the initial value of toner density of the mixture.
The initial operation must be performed only when a new developing device is inserted into the image forming apparatus. This is due to variations in the characteristics of the mixture of toner and toner carriers which occur during storage of the mixture. Thus, the image forming apparatus performs the initializing operation in response to insertion of the new developing device. However, a user may turn off the power to the image forming apparatus before the initializing operation is complete. When power is restored, it is not possible to perform the initializing operation.